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Destroyer Question: Ortho > Para?

Discussion in 'DAT Discussions' started by busupshot83, Apr 20, 2007.

  1. busupshot83

    busupshot83 S.D.N. Vet 7+ Year Member

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    Mar 22, 2003
    Texas
    Problem #15 in the Destroyer's orgo section has a Cl being added to a benzene with an activating substituent (NH). I understand activating groups direct to the ortho and para positions, but why does it say the ortho is MINOR while the para is MAJOR?
     
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  3. poc91nc

    poc91nc Banned Banned 7+ Year Member

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    Nov 5, 2006
    Could be because of steric factors...the Loudon book talks about this in ch16.
    Hmmm...the steric interaction could come from the chlorine lone pairs and oxygen on the carbonyl group. Since we are dealing with an amide, the nitrogen is predominantly sp2 and the lone pair is involved in a double bond...if you draw the corresponding resonance structure...the oxygen bears a negative charge (amides are not very reactive relative to other carboxy acid derivatives like esters and acyl chlorides since amides are resonance stabilized). So...unfavorable repulsions between the oxygen and chlorine at the ortho position might play a role in para dominance....that is the only way I can rationalize it.

    Lots of other reactions give para dominance...like nitration of bromobenzene...acylation of toluene...etc
     
  4. jdmsamurai

    jdmsamurai 2+ Year Member

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    Feb 11, 2007
    um NH is not an amide its an amine...no carbonyl but overall amide is activating
     
  5. poc91nc

    poc91nc Banned Banned 7+ Year Member

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    Ph-NHCOPh is an amide....not aniline...look at the problem.

    Aniline is more electron donating than the amide...the amide nitrogen is not as free to donate the lone pair
     
  6. poc91nc

    poc91nc Banned Banned 7+ Year Member

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    Yes...amides are activating due to electron donating...but not as good as aniline...big difference.
     
  7. busupshot83

    busupshot83 S.D.N. Vet 7+ Year Member

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    Mar 22, 2003
    Texas
    Thanks guys.
     
  8. 92CamaroLS1

    92CamaroLS1 10+ Year Member

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    Dec 7, 2005
    IL
    Ya I think its mostly steric hinderence at the ortho position. You will get both since both have the sigma framework stabilizing effect of added resonance forms, but para is less hindered so I think generally you are going to get more para.
     

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